The quality of cable t.v. pictures is of great concern to cable companies as well as to their viewers. These cable networks carry dozens of television channel signals and programs into millions of homes by transmitting the signal along a transmission line, amplifying the signal at various locations along the system to maintain the strength and quality of the transmitted signal as close as possible to the signal being transmitted at the head end or transmitting station.
There are many opportunities for extraneous signals to be picked up in line. Such impairment may arise form a variety of different sources. For example, intermodulation problems generally appear on the screen as diagonal bands that may be either narrow or quite broad depending on relationship of the intermodulation frequency with the frequency of the picture carrier. Composite triple beat impairment has video characteristics of graininess or texture effect over the entire picture. These are generally caused by overdriven cable amplifiers.
Another common problem with television transmission via cable networks is snow noise which is generally caused by a weak signal which results in a poor (small) carrier t noise ratio. Faults in the cable transmission system itself such as poor cable splices, badly coupled cable connections, or impedance which mismatch in the cable system may also result in noise.
Yet another common problem with cable t.v. reception is power line interference which appears as horizontal lines on the television screen.
No automatic television picture quality monitoring system has been available to cable television suppliers and it is believed there is no known adequate system for monitoring.
The concept of applying a Fourier transform to a signal is not new. This has been practised for many years in a variety of different industries. Similarly two dimensional Fourier transforms have been used. For example, as taught in U.S. Pat. No. 4,843,631 where it is used for pattern recognition in a pattern recognition process which, in order to locate an image content or a portion of an original image which is identical with a reference pattern, the received reference pattern or a two diminsional Fourier transform thereof is compared to the image content or portion in respect of size and orientation by inverse rotary extension with the ascertained twist angle of enlargement factor to find the position or positions at which the reference pattern when converted in that way has maximum identity with a section of the image.